The field of this invention is auxiliary wheel unit for trucks such as concrete trucks which carry extremely heavy loads.
Various state statutes and/or regulatory agencies have promulgated regulations which limit the load per tire or per axle for trucks of various types on streets and highways. Concrete trucks are one type of heavy-duty trucks which generally are subject to such regulations. It is not unusual for a concrete truck with a full load of wet concrete to exceed the regulations in some states regarding the load per tire or per axle. One known method for decreasing the load per tire on a heavy loaded concrete truck is to add additional tires to absorb some of the weight of the load. U.S. Pat. No. 3,704,896, invented by Buelow, illustrates a concrete truck mixer having a concentrated load and including conventional forward steering wheels and rear drive wheels; the concrete truck mixer is provided with additional wheels mounted on an auxiliary axle below the frame of the truck. The auxiliary axle has mounted at each end thereof tires which are interconnected by a tie rod so that the tires are joined for the purposes of rotation. The tires are mounted on the axle for turning purposes by means of king pins which rotate the tires about a vertical axis at approximately the center of the wheels. The axle assembly of the Buelow U.S. Pat. No. 3,704,896 includes hydraulic means for raising and lowering the axle assembly and air bags are provided to provide auxiliary support to the truck through the wheels and axle. In at least some designs for concrete trucks, the location of an axle such as illustrated in the Buelow U.S. Pat. No. 3,704,896 is a hindrance to the raising and lowering of the auxiliary wheel assembly due to interference between the axle and the inclined concrete transfer chute mounted at the rear of the vehicle. Further, rotation of the wheels about a vertical axis substantially running through the center of the tire such as shown in Buelow U.S. Pat. No. 3,704,896 may cause undesirable wear on the tires.
U.S. Pat. No. 3,317,193 also invented by Buelow discloses another version of a wheel assembly where several transverse supports are provided between each side of the wheel assembly. Buelow U.S. Pat. No. 3,317,193 attempts to eliminate any problem with interference between the wheel assembly and the inclined chute by making the chute retractable. U.S. Pat. No. 3,246,884 invented by Prichard et al. discloses a hinged axle assembly which serves to mount auxiliary wheels at a substantial distance from the main frame of the concrete truck and axially mounts the inclined chute with the auxiliary wheels to evidently prevent interference between the wheel assembly and the inclined chute. U.S. Pat. No. 3,497,049 invented by Duecy discloses an auxiliary wheel assembly which is mounted directly behind the truck with the wheels being joined substantially close together, the principal functions of the wheel assembly to distribute axle load and provide a balancing means to balance against a shifting side load. U.S. Pat. No. 3,912,293 of Harbers, discloses an auxiliary wheel assembly which is double hinged in order to retract underneath the chute in order to avoid the interference between the axles thereof and the inclined chute. Other patents which may be of interest include U.S. Pat. Nos. 3,944,190; 3,887,715; 3,658,303; and 3,612,491.